The manufacturing of many modern communication devices (e.g., selective call receivers), typically requires tuning an electrical circuit while measuring the radio frequency characteristics of the circuit. The tuning process is necessarily performed in substantial isolation of the external radio frequency interference (RFI) (i.e. electromagnetic interference (EMI)) commonly found in contemporary production environments. Typically, a radio frequency shielding enclosure is constructed with a hinged door which facilitates ingress and egress of the electrical circuit, while maintaining substantial isolation from the external RFI when the door is closed. Radio frequency sensors are commonly located within the RFI shielding enclosure and connected to external measurement equipment via shielded cables that typically connect through the enclosure walls.
In modern automated factories, the tuning process in many instances requires automated laser trimming of a capacitor or other element, by selectively removing a portion of the capacitor plates to change the frequency characteristics of the electrical circuit. When the electrical circuit is located within a conventional RFI shielding enclosure it is impossible to laser trim the electrical circuit's components without forming an aperture in the shield, since the laser generator itself is a source of radio frequency interference and is normally located outside of the enclosure. However, while providing at least one aperture at the enclosure allows the ingress of the laser light, it also permits external radio frequency interference to contaminate the electrical circuit frequency measurements.